This invention relates generally to threaded joints, and more particularly to threaded connections between sections of casing, tubing or drill pipe used in oil and gas wells.
In the drilling of oil, gas and like wells, it is customary to drill to the desired formation or formations, cement casing in place in the well bore and provide tubing extending downwardly in the well bore from the surface inside the casing, the annular space between the casing and tubing being packed off by a packer; although, many wells are produced without a packer. Ordinarily, the casing is perforated at the face of the formation or is set above the formation traversed by the well bore and a section of tail pipe is provided below the packer. The tail pipe may be perforated or slotted or open-ended so that, ordinarily, pore fluid from the formation flows into the well bore, such as through the perforations in the casing or below the casing and into the interior of the well bore into tubing or casing up to the surface or is pumped therethrough. In some instances, the flow is in the annular space between the tubing and the casing such, as for example, in the case of dual or multiple completions where one formation is being produced in the tubing and another formation is being produced in the annular space between the tubing and the casing.
In producing oil, gas and like wells, particularly in those wells under high pressure, joints in the tubing sometimes fail and permit oil, gas and the like to leak through the tubing into the annular space which provides a high pressure on the casing at the surface, which is the weakest point of the various strings of pipe positioned in the well bore. These leaking joints are ordinarily caused due to the failure to obtain a satisfactory seal, such as caused by normal wear and tear, improper machining and, in those joints utilizing packing, by the corrosive action of the fluid in the well bore.
It is well known in the tubing and casing arts to use a polymerized tetrafluoroethylene packing or sealing ring to assist in the sealing off of the high pressures encountered in oil and gas wells.
For example, U.S. Pat. No. 3,054,628, assigned to the assignee of the present application, shows such a ring slipped over the lower end of the pin member, and which is deformed against the tapered surface of the box member.
U.S. Pat. No. 3,047,316, assigned to the assignee of the present application, shows a seal ring engaged by the threads of the pin member, causing a portion of the seal ring to be forced into the entrance between the first two full height threads to seal the passage.
U.S. Pat. No. 2,980,451, assigned to the assignee of the present application, shows an annular groove intermediate the thread ends on either the pin member or the box member, with the seal member seated in the groove. As the threads are made up, the seal member is extruded into the threaded section adjacent the annular groove.
Although each of the foregoing prior art designs has enjoyed considerable commercial success, there has arisen the need for more uniform sealing when extruding the seal ring. The designs using the seal entrapped within the threads, in particular, sometimes experience non-uniform extrusion, and, thus, non-uniform sealing.
These same designs having the seal ring extruding into the threads also have had only a single metal-to-metal seal on one end of the entrapped seal, with the thread form on the other end of the entrapped seal ring.
It is therefore the primary object of the present invention to provide a new and improved threaded pipe joint having improved uniformity of seal ring entrapment.
It is yet another object of the present invention to provide a new and improved threaded pipe joint having the extruded seal ring completely entrapped by two metal-to-metal seals.
It is still another object of the invention to provide a new and improved threaded pipe joint which includes engagement means designed to decrease the likelihood of seal damage during makeup of the threaded joint.